1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to tape automated bonding circuits for use with ink jet cartridge assemblies in an ink jet printer.
2. Description of the Related Art
An ink jet printer may include an ink jet cartridge assembly which is carried by a movable carriage assembly in transverse directions across the width of the print medium during printing. The ink jet cartridge assembly typically includes a body, a tape automated bonding (TAB) circuit and a printhead. The TAB circuit and the printhead are each carried by the body. The printhead includes a plurality of ink jetting orifices which are in communication with ink disposed within the body, and through which ink droplets are ejected onto the print medium in known manner. The TAB circuit includes a flexible tape which carries a plurality of electrical traces. The electrical traces are connected at one end thereof with the printhead and at an opposite thereof with a contact pad in a contact pad area. The contact pads engage corresponding electrical terminals on the movable carriage assembly when the ink jet cartridge is snapped into place, and allow individual heater elements within the printhead to be actuated to eject the droplets of ink onto the print medium during use. The electrical traces on the TAB circuit are typically in the form of copper traces which are formed via an etching process on the bottom side of the flexible tape adjacent the body.
During normal printing operations and maintenance operations of the ink jet printer, ink is ejected from the ink jetting orifices in the printhead of the ink jet cartridge assembly. This jetting of the ink exposes the electrical traces on the TAB circuit to aqueous ink. The presence of the aqueous ink on the electrical traces causes the traces to corrode at a relatively fast rate. Such corrosion is obviously not desirable, and shortens the operable life of the ink jet cartridge assembly.
With certain ink jet cartridge designs, selected electrical traces on the tab circuit are exposed to nearly constant electrical bias as opposed to discrete pulsed electrical bias. Theses xe2x80x9cconstant powerxe2x80x9d electrical traces corrode several orders of magnitude faster than electrical traces with discrete pulsed electrical bias. Aqueous ink on theses xe2x80x9cconstant powerxe2x80x9d electrical traces further hastens the corrosion of electrical traces carried by the flexible tape of the TAB circuit.
Additionally, there is a trend at least within certain ink jet printers to increase the volume of the ink which is carried within the body of the ink jet cartridge assembly. Since the volume of ink is increased, the corresponding actual total power-on time necessary to empty the ink jet cartridge assembly is likewise increased. This means that the electrical traces of the TAB circuit must have an extended life when compared with throwaway designs which hold a lesser amount of ink within the body. Thus, corrosion of the electrical traces on the TAB circuit is of concern so that the operable life of the TAB circuit may be increased.
What is needed in the art is a TAB circuit which is constructed such that the electrical traces are less likely to corrode during use, thereby increasing the operable life of the TAB circuit.
The present invention provides a TAB circuit with electrical traces which are entirely coated on the bottom side with a photoimagable coating, except in the area where each trace is connected with the printhead. The tolerance of the coating at the termination adjacent the printhead is very tight when compared with conventional designs.
The invention comprises, in one form thereof, an ink jet cartridge assembly for use in an ink jet printer. A body has at least one inner ink chamber. A printhead is carried by the body and has a plurality of ink jetting orifices in fluid communication with the ink chamber. A tape automated bonding circuit carried by the body includes a flexible tape and a plurality of electrical traces. The flexible tape includes a chip window with a peripheral edge. The printhead is disposed within the chip window at a distance from the peripheral edge. Each electrical trace has a bottom side adjacent the body, a substrate held portion carried by the flexible tape, a free trace portion extending between the peripheral edge of the chip window and the printhead, and a printhead held portion connected with the printhead. The tape automated bonding circuit further includes a photoimagable coating which covers the bottom side of each electrical trace on all of the substrate held portion and the free trace portion, but does not cover the printhead held portion.
An advantage of the present invention is that corrosion of the electrical traces on the bottom side of the TAB circuit is inhibited to a greater extent than heretofore possible.
Another advantage is that the tolerance of the photoimagable coating applied to the bottom side of the traces is much tighter than heretofore possible.